Self-monitoring of blood glucose (SMBG) is important for diabetic patients to manage their blood glucose levels and to use this monitoring in treatment. Simple blood glucose self-monitoring devices using an electrochemical biosensor have recently been widely used in SMBG. The biosensor includes an insulating substrate on which electrodes and an enzyme reaction layer are formed.
Examples of enzymes used herein include glucose dehydrogenase (GDH), glucose oxidase (GO), and the like. In terms of methods using GO (EC 1.1.3.4), a problem has been noted in that dissolved oxygen in a measurement sample is likely to affect the measurement results. Methods using GDH are also not suitable for accurately measuring blood glucose levels, because although a pyrroloquinoline quinone-dependent glucose dehydrogenase (PQQ-GDH) (EC1.1.5.2 (formerly EC1.1.99.17)) is unaffected by dissolved oxygen, PQQ-GDH acts on sugars, such as maltose and lactose, in addition to glucose.
A flavin adenine dinucleotide-dependent glucose dehydrogenase (hereinafter also referred to as “FADGDH”) is unaffected by dissolved oxygen and has almost no reaction on maltose. According to Patent Documents 1 to 6 and Non-patent Documents 1 to 6, enzymes derived from Aspergillus terreus and Aspergillus oryzae, and modifications of these, are known. These enzymes, however, have relatively high reactivity to xylose (Patent Document 1), and there is therefore room for improvement in measuring blood glucose of people who are undergoing a xylose tolerance test. Further, a flavin-binding GDH having relatively low reaction on xylose (Patent Document 6), a modified GDH having a combined advantages of GO and GDH (Patent Document 7), and the like, have recently been developed; however, there is still room for improvement.